1911 Encyclopædia Britannica/Micronucleus

MICRONUCLEUS, the smaller nucleus in Infusoria (q.v.). In fission it divides by mitosis, and in conjugation furnishes the pairing or gametonuclei, by whose reciprocal fusion a zygote-nucleus is formed, which gives rise to the meganuclei and micronuclei of the individuals of the next cycle of fission.